Xen users - Aug 2008 - GPL PV: Performance issues with Xen 3.1.0 and xp64.

Hi all,

I''ve been playing around quite a bit with xen, windows and the GPL PV 
drivers... My setup is an opensuse 10.3 (xen 3.1) with two dual core 
Opteron and a raid5 (md)/ LVM setup used for domU block devices.

My problem/issue here is that, when enabling the GPL PV drivers ( /gplpv 
option ), everything seems to work fine (all pv devices get enabled, 
qemu devices get hidden and so), but the IO performance is much more 
slow than through the default qemu setup.

Usually, the raid+lvm setup give''s me a 30 MB/s sustained write 
performance... from the xp64 domU under qemu i get around 13MB/s (i''m 
using a tool called disktt that uses windows system calls to write a 
file of a certain size),  and enabling /gplpv the speed goes down until 
4MB/s or less.

Other thing i''ve seen is that qemu with an xp32 is also in the
3-4MB/s''
when writing.

I''ve tried changing the vm config from hda to xvda but the vm
doesn''t
boot , changing windows ''optimization'' options in the device,
formating
from the guest domU with different block sizes (just to try), and i get 
no performance gain''s when enabling gplpv. Tried with tap:aio devices 
created under a lvm supported filesystem, ...

Does anybody know if there''s some trick i''ve missed in the vm 
configuration or maybe the dom0 ? I don''t know what else to try :(

Here you have the vm config file for xp64, so you can check if i''ve 
something wrong.

-------------------------------------------
name="xp64sp2.base"
ostype="windowsxp"
uuid="5672033b-f819-b3a8-26fe-8876743c5112"
memory=512
vcpus=2
cpus = "2,3"
on_crash="destroy"
on_poweroff="destroy"
on_reboot="restart"
localtime=1

builder="hvm"
extid=0
device_model="/usr/lib64/xen/bin/qemu-dm"
kernel="/usr/lib/xen/boot/hvmloader"
extra=" clocksource=jiffies "
boot="c"
disk=[
        ''phy:/dev/vg_md1/lv_xen_xp64sp2_base,hda,w'',
#       ''file:/admin/ooss/xp64sp2/xp64sp2.iso,hdc:cdrom,r'',
]
#vif=[ ''mac=00:16:3e:26:00:26,model=rtl8139,bridge=xenbr0'', ]
vif=[''mac=00:16:3e:26:00:26'',]
vfb=[''type=vnc,vncdisplay=26,vnclisten=0.0.0.0,vncpasswd=vncadmin,display=0'',]
stdvga=0
vnc=1
vncunused=1
apic=1
acpi=1
pae=1
usb=1
usbdevice=''tablet''
serial="pty"
-----------------------------------------------

Thank so much, and congrats for the great job,

Juan Pablo



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